<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot>
      </slot>
    </div>
    <div class="dots">
      <span class="dot" :key="index" :class="{active: currentPageIndex === index }"
            v-for="(item, index) in dots"></span>
    </div>
  </div>

</template>

<script>
  import {addClass} from 'common/js/dom'
  import BScroll from 'better-scroll'

  export default {
    name: 'slider',
    props: {
      loop: {
        type: Boolean,
        default: true
      },
      autoPlay: {
        type: Boolean,
        default: true
      },
      interval: {
        type: Number,
        default: 4000
      }
    },
    data() {
      return {
        dots: [],
        currentPageIndex: 0
      }
    },
    mounted() {
      this.$nextTick(() => {
        this._setSliderWidth();
        this._initDots();
        this._initSlider();

        if (this.autoPlay) {
          this._play()
        }
      });

      window.addEventListener('resize', () => {
        if (!this.slider) {
          return
        }
        this._setSliderWidth(true);
        this.slider.refresh()
      })
    },
    beforeDestroy() {
      clearTimeout(this.timer)
    },
    methods: {
      _setSliderWidth(isResize) {
        this.children = this.$refs.sliderGroup.children;

        let width = 0;
        let sliderWidth = this.$refs.slider.clientWidth;
        for (let i = 0; i < this.children.length; i++) {
          let child = this.children[i];
          addClass(child, 'slider-item');

          child.style.width = sliderWidth + 'px';
          width += sliderWidth;
        }
        if (this.loop && !isResize) {
          width += 2 * sliderWidth;
        }
        this.$refs.sliderGroup.style.width = width + 'px';
      },
      _initSlider() {
        this.slider = new BScroll(this.$refs.slider, {
          scrollX: true,
          scrollY: false,
          momentum: false,
          snap: {
            loop: true,
            threshold: 0.3,
            speed: 400
          }
        });
        this.slider.on('scrollEnd', () => {
          let pageIndex = this.slider.getCurrentPage().pageX;
          this.currentPageIndex = pageIndex;

          if (this.autoPlay) {
            this._play()
          }
        });

        this.slider.on('beforeScrollStart', () => {
          if (this.autoPlay) {
            clearTimeout(this.timer)
          }
        })
      },
      _initDots() {
        this.dots = new Array(this.children.length)
      },
      _play() {
        clearTimeout(this.timer);
        this.timer = setTimeout(() => {
          this.slider.next();
        }, this.interval);
      }
    }
  }
</script>

<style lang="less" scoped>
  .slider {
    min-height: 1px;
    position: relative;
    .slider-group {
      position: relative;
      overflow: hidden;
      white-space: nowrap;
      .slider-item {
        float: left;
        box-sizing: border-box;
        overflow: hidden;
        text-align: center;
        a {
          display: block;
          width: 100%;
          overflow: hidden;
          text-decoration: none;
          img {
            display: block;
            width: 100%;
          }
        }
      }
    }
  }

  .dots {
    position: absolute;
    right: 0;
    left: 0;
    bottom: 12px;
    text-align: center;
    font-size: 0;
    .dot {
      display: inline-block;
      margin: 0 4px;
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: white;
      opacity: 0.5;
    }
    .active {
      width: 20px;
      border-radius: 5px;
      opacity: 0.8;
    }
  }

</style>
